VSS Correct, however mileage wrong.

[asmi]

Hi there guys,

I have already managed to calibrate the speed in accordance to my vehicle however the mileage is wrong in MPGuino.

I build my own PCB mpguino, however I used a 20Mhz crystal instead of 16mhz.

Is this the reason why my mileage is wrong in mpguino?

My ATMega328 was bootloaded on Duemilanove, and I saw the crystal on it was 16Mhz.

[asmi]

Ohyeah, One more issue.

What is Current, Tank and Instant?

[ngrimm]

Greetings. Are you saying the miles displayed on the MgGuino do not match the actual miles driven or are you saying the miles per gallon are wrong?

[asmi]

I am using the canadian metric version version 0.81. It shows the vechicle speed as well as the mileage. However both doesn't tally. When the speed is correct, the mileage is wrong. When the mileage is correct, the speed is wrong.

[ngrimm]

I am just another user but I can imagine the different clock speed could change the speed readout. As you probably know, miles or kilometers per gallon would be based on distance so and not speed so I think that is most important. Instant means mpg/kpg (liter) at that point in time, Current is mpg/kpg achieved on the current trip (you can change how many seconds it takes to reset the current trip if the engine has been switched off). Tank is mph/kpg since you last filled the tank. You can reset Current trip by pressing the center and the right button together and reset Tank by pressing center and left buttons together. By the way, pressing the right button step through the menus one direction and the left button steps through the menus in the opposite direction. These are just some things it took me a while to figure out. Norm

[asmi]

Great! Thank you.

I might try a different clock speed to see if I can get the same speed readout.

[gtkid2002]

Really hate ressurecting a really long dead thread, but I'm having the exact same issue, except I'm using the proper clock chip.

I can either have my speed horribly fast at vss count of 8305, or have it be accurate at somewhere around 13000. It's an 04 Honda Civic. I know I have the wires right, and I know that the car is reading accurate speeds (I know when I'm doing 90mph, and when I'm doing 65 ).

So, any ideas on where I should be looking?

[nickdigger]

I'm not sure if the question was ever answered: "What values are you looking at?"

If speed and odo-distance are accurate, then your VSS & config are good.
If only speed OR odo is good, and the other bad, then i guess the crystal MHZ could be a factor, but only if the values are wrong by 25%.